In recent years, there have been various proposals concerning a dynamic pressure bearing apparatus used to support various rotors such as a magnetic disk, a polygon mirror or an optical disk at a high speed. The dynamic pressure bearing apparatus, is applied to, e.g., such a motor as shown in FIG. 16, a bearing sleeve 2 as a bearing member is fitted to a shaft member 1 so as to be capable of relative rotation, and a radial dynamic pressure bearing portion RB is formed by injecting a lubricating fluid such as an oil into a predetermined very small gap formed by arranging a dynamic pressure surface provided on an outer surface of the shaft member 1 and a dynamic pressure surface provided on an inner surface of the bearing sleeve 2 so as to be opposed to each other in close proximity in the radial direction. Moreover, a dynamic pressure surface provided on a thrust plate 3 fixed to the shaft member 1 by tight fitting and a dynamic pressure surface on the bearing sleeve 2 and a counter plate 4 are oppositely arranged in close proximity to each other in the axial direction so as to form a predetermined very small gap, and a lubricating fluid such as an oil is injected into the small gap, thereby constituting thrust bearing portions SBa and SBb.
In addition, a pressure is applied to the lubricating fluid by the pumping action of dynamic pressure generating grooves (not shown) provided on at least each one of the opposed dynamic pressure surfaces of the radial dynamic pressure bearing portion RB, the thrust dynamic pressure bearing portions SBa and SBb so that a dynamic pressure is generated respectively, and both the shaft member 1 and the thrust bearing members 3 and 4 are rotationally supported while relatively floating in the radial direction and the thrust direction by the dynamic pressure.
Such a radial dynamic pressure bearing portion RB and thrust dynamic pressure bearing portions SBa and SBb are generally separated from each other and arranged in this manner. Therefore, when the lubricating fluid is independently filled in each dynamic pressure bearing portion, a quantity of the lubricating fluid is reduced as a whole, and the lubricating fluid is deteriorated due to oxidation or gelation or becomes insufficient due to evaporation or the like. As a result, the duration of life of the bearing is shortened, and there occurs a problem that the lubricating fluid is apt to leak due to a change in pressure or a change in temperature.
Based on the above fact, there has been developed a dynamic pressure bearing apparatus which can continuously fill the lubricating fluid in the entire area of the bearing gaps from the radial dynamic pressure bearing portion RB to the thrust dynamic pressure bearing portions SBa and SBb and increase a quantity of the lubricating fluid.
However, even if the entire area of the bearing gaps is completely filled with the lubricating fluid, air bubbles may be possibly generated at a negative pressure part produced in the bearing portion. Therefore, there is the risk that the lubricating fluid may be pushed toward the outside of the bearing by the air bubbles and the lubricating fluid may leak to the outside.